[RE-wrenches] Off-Grid Whole House RO

[Jason Szumlanski]

That is what I was thinking, that the RO booster pump doesn't need a lot of
pressure on the inlet side. There is a lot of wastewater, but I have not
calculated the ratio. My visual analysis is that is it more like 6:1 or
more. The production level is very low, perhaps 1-2 gallons per minute. I
would love to not have a well pump running at all when producing RO,
pumping raw water into a holding tank in advance of RO production. I don't
think the owner is opposed to managing this manually, but it could also be
set up on a solar direct DC pump or on a smart load output of the inverters
if using an AC pump.

The house does have rainwater catchment that is great in the summer,
producing 100% of its needs. However, the property is more heavily used in
the dry winter months. So the rainwater system doesn't align with the use
case for the home (vacation/second home in the nice season in Florida).

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208


On Thu, May 8, 2025 at 3:22 PM Jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi Jason
>
> What’s the actual water output from
> The RO? We had one at our house before I took it out and replaced the
> house water with rainwater catchment. 3 yrs and counting in the high
> desert.
> I couldn’t live with the 2-3 to 1 loss ratio.
>
> A few options as I suspect the actual RO output is closer to 1-2 gpm.
> 1. Use a 1/3hp well pump into a large pressure tank with relatively low
> pressure switch.  You might even get away with a small sump pump. The RO
> should t need but minimal input pressure
>
> 2. Assuming the RO system doesn’t need rhe 1.25hp pump ( i  am assuming
> the RO goes into a tank and much then has a pressure pump to supply the
> house. If it doesn’t I would recommend installing said design) I’d install
> a smaller motor and pump head to better match the RO flow rate.
> You could look at getting a high efficiency DC pump or 3 phase with vfd.
> Sun pumps has such things.
>
> Jay
>
>
>
> > On May 8, 2025, at 12:38 PM, Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
> >
> > 
> > Water pump is not my strong suit. I usually leave that up to the experts
> around here. Unfortunately, the experts are clueless when it comes to
> off-grid living. I have a client with a setup that is pretty unworkable.
> I'm trying to give him some general guidance.
> >
> > The setup uses a brackish water (might as well be salt water) very
> shallow well. It is about 3 ft underground for the water table. The RO
> system installer has a 1 HP 1.25 SF Century centrifugal surface pump
> drawing water from the well and pressurizing the inlet of a StaRite 1.25 HP
> booster pump designed for about 10 GPM at 150 PSI to run water through the
> RO system.
> >
> > Both of the pumps run simultaneously and continuously when producing
> water, and the water production is ridiculously low. I understand that RO
> production is going to be slow, but the amount of power these pumps are
> using is pure insanity. I have advised the client that, at a minimum, this
> system needs to be on a smart load circuit to run only when there is
> adequate battery capacity. The startup surgery is not a concern, but it
> does flicker the lights and it makes quite the racket.
> >
> > My thoughts are that the well pump is drastically oversized. The booster
> pump only needs 10 gallons per minute, and it has a suction head of 15 ft.
> I don't even know if the well pump pressurizing the booster pump inlet is
> required. I'm thinking we should be slow pumping water into an interim
> holding tank at least at the height of the booster pump. At a minimum, the
> well pump should be on a pressure switch with pressure tank so it can
> cycle.
> >
> > Can anyone give me some general guidance, and perhaps a VFD pump that
> does not have the startup surge and is maybe more efficient? During times
> of heavy use, the RO system can easily eat up half of the PV produced
> during a day at this site.
> >
> >
> > Jason Szumlanski
> > Florida Solar Design Group
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